28V, 2A Buck Constant Current Switching Regulator for White LED

Transcription

1 28V, 2A Buck Constant Current Switching Regulator for White LED FP7102 General Description The FP7102 is a PWM control buck converter designed to provide a simple, high efficiency solution for driving high power LEDs. With a 0.25V reference voltage feedback control to minimize power dissipation, an external resistor sets the current as needed for driving various types of LEDs. The FP7102 includes a high current P-MOSFET to realize high efficiency and excellent transient characteristics. The PWM control circuit is able to change the duty ratio linearly from 0 up to 100%. Other features include user accessible EN pin for enabling, thermal shutdown, cycle-by-cycle current limit and over current protection. Features Wide Supply Voltage Operating Range: 3.6 to 28V Built-in P-MOSFET for 2A Loading Capability Precision Feedback Reference Voltage: 0.25V (2%) Low Current Consumption: 4mA Internal Fixed Oscillator Frequency: 320KHz (Typ.) Internal Soft-Start Function (SS) Over Current Protection Package: SOP-8L &SOP-8L(EP) Typical Application Circuit V IN VCC LX FP 7102 LX ON/OFF EN COMP GND GND 1/12

2 Function Block Diagram VCC EN Reference Regulator Enable Control 2.50V Oscillator Over Current Protection 0. 25V 36K 500 Output Drive Control Circuits COMP Internal Soft Start Circuit Thermal Shutdown GND GND LX LX 2/12

3 Pin Descriptions SOP- 8L FP7102 9Fa-86L Name No. I / O Description 1 I Error Amplifier Inverting Input EN 2 I Enable Control COMP 3 O Error Amplifier Compensation Output V CC 4 P IC Power Supply (PMOS Source) LX 5 P PMOS High Current Output LX 6 P PMOS High Current Output GND 7 O IC Ground GND 8 O IC Ground SOP- 8L (EP) Top View 1 8 GND Name No. I / O Description EN COMP VCC FP7102 9Fa-86L GND LX LX 1 I Error Amplifier Inverting Input EN 2 I Enable Control COMP 3 O Error Amplifier Compensation Output V CC 4 P IC Power Supply (PMOS Source) LX 5 P PMOS High Current Output Bottom View LX 6 P PMOS High Current Output GND 7 O IC Ground GND 8 O IC Ground EP 9 P Exposed PAD. Must connect to LX EP 3/12

4 Marking Information SOP- 8L & SOP-8L (EP) Halogen Free: Halogen free product indicator Lot Number: Wafer lot number s last two digits For Example: TB 86 Internal ID: Internal Identification Code Per-Half Month: Production period indicated in half month time unit For Example: January A (Front Half Month), B (Last Half Month) February C (Front Half Month), D (Last Half Month) Year: Production year s last digit 4/12

5 Ordering Information Absolute Maximum Ratings IR Re-flow Soldering Curve FP7102 Part Number Operating Temperature Package MOQ Description FP7102DR-LF -25 C ~ +85 C SOP-8L 2500EA Tape & Reel FP7102XR-LF -25 C ~ +85 C SOP-8L (EP) 2500EA Tape & Reel Parameter Symbol Conditions Min. Typ. Max. Unit Power Supply Voltage V IN 28 V Output Source Current 2 A Error Amplifier Inverting Input V Allowable Dissipation T A mw Thermal Resistance Junction to Ambient Thermal Resistance Junction to Case ESD Susceptibility θ JA +175 / W θ JC +45 / W HBM (Human Body Mode) 2 KV MM (Machine Mode) 200 V Storage Temperature Lead Temperature (soldering, 10 sec) /12

6 Recommended Operating Conditions Parameter Symbol Conditions Min. Typ. Max. Unit Supply Voltage V IN V Operating Temperature DC Electrical Characteristics (V CC =6V, T A = 25, unless otherwise noted) Reference Parameter Symbol Conditions Min. Typ. Max. Unit Output Voltage V REF connected to COMP V Input Regulation V REF V CC =3.6 V to 25 V mv Output Voltage Change with Temperature Oscillator Section V REF / V REF T A =-25 to T A = 25 to Oscillation Frequency f 320 KHz Frequency Change with Voltage Δf / ΔV V CC =3.6V to 25V 5 % Frequency Change with Temperature Error Amplifier Section Δf / ΔT T A = -25 to % Input Bias Current I B μa Voltage Gain Av 100 V / V Frequency Bandwidth BW Av=0 db 6 MHz Output Voltage Swing Positive V POS V Output Voltage Swing Negative V NEG V Output Source Current I SOURCE V comp =200mV μa Output Sink Current I SINK V comp =200mV μa Idle Period Adjustment Section Maximum Duty Cycle T DUTY V =0.2V 100 % Output Section PMOS D-S Voltage V DSS V COMP =0.1V -20 V PMOS Source Current I D -2 A PMOS On Resistance R V CC=5.0V, V =0V DS (ON) V CC =10V, V =0V Output Leakage Current I L 5 μa Thermal Shutdown Section Thermal shutdown Temperature 150 Over Current Protection Section PMOS OCP Current I OCP 3 A % mω 6/12

7 Parameter Symbol Conditions Min. Typ. Max. Unit Total Device Section EN Input Current I EN EN pin Open 20 μa Upper Threshold Voltage (EN) V UPPER 1.12 V Lower Threshold Voltage (EN) V LOW 0.87 V Hysteresis V HYS mv Average Supply Current I AVE 4 6 ma V CC Shutdown I SHUTDOWN 15 μa 7/12

8 Detailed Description Voltage Reference A built-in 2.5V reference regulator supplies FP7102 internal circuits. Also, this 2.5V reference voltage is divided down by an internal resistive divider to provide a 0.25V precision reference voltage to the error amplifier non-inverting terminal. Setting the LED Current FP7102 is a constant current buck regulator. The LEDs are connected between V OUT and pin as shown in the Typical Application Circuit section. The pin is 0.25V in regulation. Therefore, the LEDs current I F is set by V and the resistor R 2 connected between and ground by the following equation: V IF R 2 I F should not exceed the 2A current capability of FP7102 and therefore R 2 minimum value must be approximately 0.13Ω. Output Voltage The output voltage is primarily determined by the number of LEDs(n) connected between V OUT and pin. Therefore, V OUT can be written as: V OUT ((n V ) V F ) Where V F is the forward voltage of one LED at the set LED current level (see LED manufacturer datasheet for forward characteristics curve) Oscillator The fixed PWM frequency is generated by an internal oscillator. Its typical values are 320KHz. Thermal Protection The thermal protection is triggered when junction temperature is higher than 150 that may occurs by an abnormal heavy current loading. When this happens, the FP7102 turns output off. Once the junction temperature is cooled down to lower than 130, FP7102 starts again and turns the power switch on. 8/12

9 Over Current Protection The FP7102 uses cycle-by-cycle current limit to protect the internal power switch. During each switching cycle, a current limit comparator detects if the power switch current exceeds the internal setting current. If it does, over current protection function decrease the oscillator frequency to prevent thermal issue. 9/12

10 Typical Application FP7102 1W / 3W LED for DC Input Circuit Dimming Control Circuit Changing the duty cycle of PWM signal can get different LED current. The PWM signal is recommended above 10kHz. The application circuit is shown in the following. The LED current can be calculated by the following equation: I LED V R4 (V PWM Duty V R3 R5 R2 ) 10/12

11 Package Outline SOP-8L UNIT: mm Symbols Min. (mm) Max. (mm) A A A D E H L θ 0 8 Note: 1. Package dimensions are in compliance with JEDEC outline: MS-012 AC. 2. Dimension D does not include molding flash, protrusions or gate burrs. 3. Dimension E does not include inter-lead flash or protrusions. 11/12

12 SOP-8L (EP) UNIT: mm Symbols Min. (mm) Max. (mm) A A A D E H L θ 0 8 Exposed PAD Dimensions: Symbols Min. (mm) Max. (mm) E REF D REF Note: 1. Package dimensions are in compliance with JEDEC outline: MO-178 AA. 2. Dimension D does not include molding flash, protrusions or gate burrs. 3. Dimension E does not include inter-lead flash or protrusions 12/12